This invention relates generally to protection mechanisms and more specifically to failure protection within a communication system.
Communication systems have become of critical importance within today""s society. With this increase in importance comes a need for communication infrastructures to maintain a higher reliability and signal quality. To create these higher standards many techniques have been implemented. One extremely successful and wide spread method to maintain the integrity of communication networks, even during problem time periods, is through the use of redundant communication channels.
The use of redundant channels allows communication links traversing a primary channel to be transferred to an alternative channel when problems occur with respect to the primary channel. Utilizing this technique are fibre optic communication links, each typically comprising a working channel and a protection channel that are physically identical in bandwidth and functionality. In normal operations, with no faults indicated on either channel, the communication path is chosen to be through the working channel. In cases that a problem is indicated concerning the working channel with no problem indicated on the protection channel, the particular communication link is redirected via the protection channel without interrupting the actual transmission of information.
Within the fibre optic communication system, a decision procedure is performed to determine which of the physical channels, those being the working and protection channels, the transmission of information signals is to traverse. In order to decide which channel to utilize, the decision procedure is input with statuses corresponding to the individual channels. These statuses indicate the priority of any problem that might be associated with the transmission on the particular channels. The decision procedure selects for transmission the channel with the lower priority failure level in circumstances in which the working and protection channels have problems of different priorities.
Failures include, but are not limited by, solid signal failures and high bit error rates. An area of difficulty with the decision procedure exists in cases where two error types have the same priority. In such cases, the decision is made not on which error causes the least disturbance in the communication link, but on predetermined decision criteria. These decision criteria may include selecting the working channel over the protection channel in cases of equal priority failures or selecting the transmission channel that declared the most recent failure.
Unfortunately, there are circumstances that exist where signal failures that have the same priority due to a standard convention should in fact be defined with separate priorities. One case of this exists with respect to oscillating failures versus solid signal failures. An oscillating failure typically occurs on a fibre optic channel due to an equipment failure while a solid signal failure typically occurs due to a fibre and/or equipment failure. An oscillating failure can be seen as an intermittent solid signal failure. When an oscillating failure is in the failure state of the cycle it is recognized by the decision procedure as a high priority failure similar to that for a solid signal failure. Due to the consistently changing state of the problem within a fibre optic channel suffering from an oscillating failure, it is well understood for a decision procedure to lock an oscillating failure as a high priority failure if a predetermined number of cycles are detected within a predetermined amount of time.
The problem, in this case, exists if one channel is locked into a high priority failure state due to an oscillating failure and the other channel has a solid signal failure. Communication on the channel with the oscillating failure would be preferred over the channel with the solid signal failure for it would at least function properly for intermittent periods of time. Unfortunately, according to one prior art decision procedure in which the last channel to declare a high priority failure state is preferred, the communication link would continue to traverse the channel with the solid signal failure if the last channel to go to a high priority error state was the channel with the solid signal failure. According to another prior art decision procedure in which the working channel is always preferred over the protection channel when both channels are in a high priority failure state, the communication link would continue to traverse a working channel with a solid signal failure if the protection channel is locked into a high priority state due to an oscillating failure.
Therefore, a method for making channel selection decisions is needed that is flexible while compensating for different problems on the communication channels. This procedure must adhere to the standards established for the failure protection in the particular communication medium, but allow for, in particular, a solid signal failure to take priority over an oscillating failure.
It is an object of the present invention to overcome the disadvantages of the prior art and, in particular, to provide a system and method by which different failures are treated with different priorities.
According to a first aspect, the present invention provides a control apparatus capable of being implemented within a switching card coupled to at least two signal transmission means, the control apparatus being input with input line conditions (ILCs) with respect to one of the two signal transmission means and outputting corresponding output line conditions (OLCs) with use of line condition control (LCC) logic operating within the control apparatus; and wherein the LCC logic is capable of setting the OLCs equal to a first failure priority condition that is less than a maximum failure priority condition if a protection oscillation control (POC) mechanism is activated, activating the POC mechanism for a hold time if an oscillation criterion is met, and setting the OLCs equal to the corresponding ILCs if the POC mechanism is not activated.
According to a second aspect, the present invention provides a switching card incorporating the control apparatus of the first aspect, the switching card, capable of being coupled to at least two signal transmission means, further comprising a decision apparatus that takes as inputs the OLCs output from the control apparatus and selects which of the transmission means to be used for transmitting information signals with use of decision logic operating within the decision apparatus.
According to a third aspect, the present invention provides a switching card incorporating first and second control apparatuses according to the control apparatus of the first aspect, the switching card, capable of being coupled to working and protection signal transmission means, further comprising a decision apparatus that takes as input first and second OLCs output from the first and second control apparatuses respectively, the first and second control apparatuses taking as input first and second ILCs corresponding to the working and protection signal transmission means respectively; and wherein the decision apparatus selects which of the working and protection signal transmission means to be used for transmitting information signals with use of decision logic operating within the decision apparatus.
According to a fifth aspect, the present invention provides a bi-directional line switch ring (BLSR) system incorporating a plurality of communication systems according to the third aspect in which the communication systems are connected in series with a first communication system coupled directly to a last communication system.
According to a fourth aspect, the present invention provides a communication system incorporating first and second switching cards according to the third aspect, the communication system further comprising first and second port cards coupled to the first and second switching cards respectively, and first and second signal transmission means coupled independently between the first and second switching cards.
According to a sixth aspect, the present invention provides in a control apparatus capable of being implemented within a switching card coupled to at least two signal transmission means, a method of controlling output line conditions (OLCs) with use of corresponding input line conditions (ILCs), the method comprising the steps of: setting the OLCs to a first failure priority condition that is less than a maximum failure priority condition if a protection oscillation control (POC) mechanism is activated; activating the POC mechanism for a hold time if an oscillation criterion is met; and setting the OLCs equal to the corresponding ILCs if the POC mechanism is not activated.